Fish scales were obtained from frozen fish collected by fishermen and Department of Fisheries and Oceans research personnel, as well as from sediment core samples. Some scales were also collected from trypsin-treated fish; a standard method used for the digestion of tissue. The scales were processed and identified at the Pacific Geoscience Centre/Institute of Ocean Sciences in Sidney, British Columbia. Some additional slide material was also borrowed from the Bone Lab at the University of Victoria, British Columbia, and used as a reference for scale identification.
Scales were removed from frozen specimens in the A, C, E, G, I, and J regions of selected fish (Casteel, 1976). Effort was taken to remove as much tissue from the scales as possible without damaging the scale. Additional care must be taken to remove all tissue from fish that have a high oil content as this can damage the scale. Scales were then allowed to air dry. Next, they were gently sonicated in a dilute solution of a laboratory grade detergent (a standard jewelry-store type of sonicator will work) for approximately 30 minutes. Scales were then rinsed in freshwater and under a dissecting microscope, any remaining tissue was gently scraped off with a scalpel. Fish with a high oil content that were not properly cleaned in the previous step were difficult to scrape as the oily residue, once dried, did not soften or easily rehydrate. At this stage scales were either stored dry in plastic sample bags or mounted for subsequent microphotography.
Sediment samples were placed in a 1L glass beaker with a few grams of sodium metaphosphate and enough water to allow the sample to disperse into a slurry. Samples were gently stirred and broken up with a plastic spatula to speed the process. The sample slurry was then allowed to sit for approximately 30 minutes. Next, samples were then sieved through a 250 m sieve, and the residue was stored in 70% isopropyl alcohol or 70% ethanol. Fish scales and bones, as well as other biogenic remains, were separated and identified using a dissecting microscope at relatively low power. Separated material was then tallied and stored in 70% ethanol. Figures of preserved scales are presented in downcore order from Effingham core B03 (for details see Dallimore, 2001).
There are various methods used to mount fish scales. Methods utilizing mucilage were difficult to implement for this research, particularly when mounting many small scales per slide. It was found that the scale with the mucilage mixture dried very rapidly, causing the scales to curl before a cover glass could be laid down. However, other fish laboratories have successfully used this method. We found that the easiest mounting method was to allow the scales to sit in freshwater for a short period of time (<15 minutes). Once they had become flexible, the scales were mounted between glasses. Pairs of standard laboratory glass slides as well as the 2 cm x 2 cm glass slides used in making 35 mm slide mounts were found to be suitable. Care was taken to keep scales moist so that they did not curl or fracture prior to positioning the cover slide.
Using a dry mounting methodology is conducive to examination using both reflected and transmitted light microscopy. Although acetate peels also permit microscopic examination, many of the preserved scales are likely too fragile for the pressing process. In the case of the 35 mm slide mounts, these can also be projected onto screens using a standard projector and an appropriate slide carousel. These mounts can also be used in a microfiche reader, and printed out, greatly facilitating the identification of features critical to taxonomic assignment.
A shortcoming of dry mounting is that if there are scales of varying thickness on a mount, there is potential for the scales to move around under the glass. Care must also be taken with transportation of dry mounted slides as they can easily be broken. The metal brackets utilized in preparing micropaleontological research slides are particularly useful in securing glass laboratory slides together. Transparent adhesive tape was also used along the edges of the glass to secure some slides together. `Magic'-type tape is preferred, as it leaves no gummy residue on the glass and can easily be removed. When using this method some areas along the edges were left open to permit any remaining water residue to evaporate. Once completely dry, the edges were sealed with tape. To facilitate drying, a heating plate on a low setting can be used. Tape should only be used for slides that will be reopened again as the relatively short life spans of these sealants make them unsuitable for archival purposes. Dry mounted scale preparations are susceptible to desiccation cracks and the additional problems described above. In addition, for long-term preservation, we suggest use of water-soluble mounting media such as gum tragacanth, commonly used by foraminiferal researchers, or a non-solvent media such as Entellan.
Microphotography digital image capture of the preserved fish scales was carried out using an Olympus SZH10 Research Stereo Microscope and a Polaroid Digital Microscope Camera at generally low magnification. Dimensions of scales were measured under the microscope, and scale bars were then digitally added to the images. All scales for publication were photographed using transmitted light to produce the characteristic "fingerprint" image. Some scales were initially also photographed with reflected light using a fiber optic light source. This method was quickly abandoned because it was difficult to achieve the desired light level and image quality. The digital images were then rendered on a Macintosh computer using Adobe Photoshop 6.0 software.